Telegraph system



v 1,672,998 L. M. CLEMENT TELEGRAPH SYSTEM Filed Dec. 5 1921 .2 l??eets-Sheet ky fl/w 71 June 12, 192&

' L'. M. CLEMENT v TELEGRAPH mm filed Dec. 5, 1921 d 2 Sheets-Sheet 2 fig; F/q. a. 55 1 V /n|/enfo/ [aw/S M C/emehf v y My fill Patented June 12, 1928 UNITED STATES PA"l ]51l\lT or f ce,

LEWIS CLEMENT, on NEW YORK, N. Y., Assrenon "10. wnsrnnn nnncrrnic com- PANY, m'conronunn, or NEW YORK, N. y.,aconronarron or'nEwYonK;

ELEGRAPH SYSTEM.

Application filed December This invention relates to a telegraph sys: temand more particularly to an arrangement wherebytelegraph signals; may be transmitted without interference from strays or static. Y I

It has been proposed in carrier wave signaling to employ two sources of different frequency alternating currents i within the audible range and to cause these currents to be alternately applied to modify the carrier wave in regulainsequence for,calling pur poses. The transmission station is rovided with .means to cut off the local tal ing circuit from the outgoing carrier channel and to connect in its stead to the outgoing channel, a source for alternately applying two alternating currents of different frequency 1n regular sequence. These alternately applied currents are caused to modify the outgoing carrier wave in the same manneras it is modified by speech currents when carrier telephony is in progress. At thepreceiving station the modulated carrier wave is detected or demodulated and the detected alternate frequency currents are caused to energize 'selectivecircuits to control the operation of a differentially acting relay which in turn operates the local signal element or applies ringing current to the receivingcircuit as the case may be. i i i The present invention has for one of its features the use of Waves of different frequencies alternating at a definite rate or shift fretpiency for telegraph. signaling. In si nal transmission systems there is frequent y a tendency for interference to occur due to static energy or other strays, particularly in certain latitudes and during certain times of the year; In fact, it has beenconsidered practically impossible to free teledynamic operation from interference under the conditions stated above. i

According to the present invention a signaling system is provided at its transmission station with means to supply two'sets of waves of different frequencies and alternating at adefinite rate or shift frequency to constitute signal impulses. Thesets of waves may be either high frequency waves adapted to be radiated, low. frequency waves designed to modulate a CitlI1Bl W2lV6, the modulated high frequency wave being transmitted, or low frequency waves which'may be transniittedover a line. y y if y ;At the receiving station the incoming 5, 1921. Serial no. 519,865.

waves of different frequencies are separated byselective circuits or filters and used to produce oscillating currents which are rectified. The rectified impulses, alternating at the definite rate .are su plied to means controlling a signal trans ating device or indicator having associated therewith means selective of the meet alternation of the impulses, The latter .meansmaybe either an element of the translating. device tuned to the shift frequency, such as a tuned reed, or a circuit selective of energyotthis frequency included in the connections between the con-..

trol device and thesignal translator. .l'lhe signal translating device may beatelep'lione receiver. By making theysi al receiving device responsive only to the oint action of the signal waves ofpredetermined frequen cies applied at a definite rate of alternation, which should preferably,but not necessarily, be within theaudible range,,thc possibility of false signals beingreceived is remote; r The primary object ofthisinvention isto provide a telegraph systemwhich will .be free from interference due to strays or static. Another object isto: provide. atelegraph system employing oscillatory currents ofgtwo frequencies alternating at a-definite frequency or rate toiidentify the signal impulses constituting messages transmitted between these stations; Q

A feature is the provision of means wherebyincoming signal waves of different frequencies alternatingat adefinite frequency or rate may control the operation of a signal translating device. For an understanding ofra signal system operating accordingto this invention and embodying its. principles, reference. may be made to the accompanying detailed description taken in conjunctionwiththeannexed drawings, in which Fig. 1 illustrates a radio transmitting. station adapted to radiate two high frequency waves alternating at a definite frequency; Fig. 2shows-a station designed to transmit waves of one.frequency modulated by two waves oddifferentsfre quencies alternating ata definite rate; Figs. 3. 4, 5 and 6 illustrate differentreceiving circuit arrangements which may be used with Bil source. of! oscillations comprising. apair of three-element electric discharged-devices 1 is adapted to be driven to open andfclose other frequency, for example, 2000 cycles will be provided. While the frequencies for the modulating source are given above as.

within the audible range,-it maybe stated thatthey are not limited to such range.

The. plate circuit-of the oscillator is coupled by a transformer 22 to the grid-filament circuit of athree-element electric discharge modulator 20, which also includes a source of high frequency current 21. The secondof the transformer 22 has a condenser 23 connected in parallel with it to constitute a circuittuned broadly to the frequencies supplied bythe oscillator 15.

The plate circuit ofthe modulator 20 is associatedwith .thetinput circuit of an. amplifier 24, which is merely symbolic of the fact that amplification is 1 desirable, and hence any amplifying system including any number of amplifiers maybe used. The out? put circuitof the amplifier is associated with the antenna 25. i i i As described above, a key, relay, or other well-known controller13 may be inserted in the oscillator circuit system,hereinshown as connected in the parallel circuit including the condenser 18 and commutator 19, to control the signalenergy radiated from the antenna 25. i i

Fig. 3 shows a receivin station for use with the transmitting'station illustrated in Fig. 1 having two: receiving circuits associated with an antenna circuit. The antenna circuit 26 is given two degrees of freedom and includes two inductance coils 27 and 28. These coils are respectively associated with tuned circuits 29 and 30 included in the input circuits of two detectors 31 and 32, each of which is also supplied with high frequency currents by the local sources 33 and 34. These sources each supply oscillations of a frequency differing from the incoming waves by a frequency within or without the audiblerange, for example, 1000 cycles per second. i r I Thus, if the incoming frequencies are f and f the'source 33 will supply a current of frequency 7 11000 and the source 34 will supply a frequency of f i1000 and as a result there will be present in the output circuits of the detectors 31 and 32 impulses of natingrat a shift frequency determined by the interrupter or commutator 12 of, the transmitting station. These impulses, after amplification by the amplifiers 35, arerectified by the unidirectional devices 37.; The rectified impulses, succeeding each other at the shift frequency, are transmitted through separate primary windingsqof the trans former 38 to inducecurrent in its secondary, which is shunted by a condenser 39 to constitute a circuit tuned to the shift frequency.

The primary windings ofthe transformer 38 should be so connected that impulses supplied to them, if of the same amplitude and applied simultaneously, would not produce a voltage across its secondary winding. On the other hand, signalcurrents supplied to these windings alternately at the shiftlfra quen'cy of the transmitter interrupter will set up an alternating voltage of} this frequency in the turned circuit constituted by the transformer secondary winding andthe condenser 39. t Thisjvoltage will be: impressed upon the grid element of the device 10 and because ofthe amplifying properties of the device 10, a current of large amplitude will flow through its plate circuit which will be transferred by the transformer 41 to the signal receiver 42 j q i If a disturbance due to strays or static is received, circuits 29 and 30 will probably the difference frequency, namely, 1000,alter have oscillations of their natural frequencies set; up in them and currents will fiowsimultaneously through. both primary windings of the transformer 38. balance one another and will produce no effect in thereceiver. However, should any unbalance occur, the receiver will not be ac tuated. unless a voltage of the shift frequency, to which the selective circuit in- 1 cluded in the inputcircuit of the tube 40 is tuned, is produced in the secondary winding ofthe transformer. i U s i A slightly difierent circuit arrangement for a receiving station of this type is shown in Fig. 4. Thisarrangement is adapted for usewith a systememploying two waves of different radio frequencies closely spaced in the frequency spectrum, and a single local source is employed to produce the beat frequency impulses.

Inthis system two sets. of radio frequency waves, which may be of the order of 310,000 and 300,000 cycles, are transmitted from the distant station. At the receiving statiomantenna 43 is tuned toreceiveboth sets of waves which are transferred to theinput cir-. cuit of the detector. 44 by the transformer 45, the secondary winding of which is shunted by a variable condenser to constitute acircuittuned broadly to the same band of frequencies as the antenna.

. Associated with the input circuit of the detector is a source of local oscillations 46 There will, therefore, be

supplying oscillations of say 250,000 cycles. present in the output circuit of the detector 44 oscillations of the difference frequencies 50,000 and 00,000 cycles which may be selected by the tuned circuits or filters 47 and 48, respectively, separately impressed upon the input circuits of the amplifiers 49 and 50, rectified by the unidirectionaldevices 37 and transmitted to the receiver "circuit as described above. Since the selected waves alternate at the shift fre quency, an alternating current of this frequency will be supplied to the receiver 42.

Another method 'ofutilizing radio frequency waves to produce an alternating current of; shift frequency in the receiver circuit is shown in Fig. 5. In this figure there is shown a receivin station which embodies an antenna system 3 having two degrees of freedom and a pair of separate tuned circuits or filters 54 and 55 associated therewith, selective of the two sets of high frequency waves.

The incoming waves are selected by the timed circuits or filters 54 and 55, amplified by the amplifiers 56, rectified by the rectifiers 37, the circuit terminals A and B of which are connected to the correspondingly lettered terminals in this figure, and supplied to the receiver circuit 3842 hereinbefore described.

As in the preceding arrangements the incoming waves alternate at the shift frequency rate and 35a consequence the rectified impulses produce an alternating current of the shift frequency in the receiver circuit to operate thet'ranslating device 42, which may translate the signal into sound either by the use of a telephone receiver or a rectifier and relay controlling an "ordinary telegraph sounder or other signal translator. For example,a rectifier and relay may be connected in the secondary circuit of the transformer 41, the armature of the relay being adapted to control a local circuit including a sounder.

Referring'now to Fig. 6," there is illustrated a receiving station adapted for use with the transmitting station shown in Fig. 2. The incoming signal modulated waves incident upon the antennav 58 are detected by the three-element electric discharge device 59; the detected im 'ulses of the alternate frequencies are amp ified by the amplifier 60. separated by the selective means 61 and 62 and rectified by the unidirectional de-' vices 37. The resulting impulses, alternating at the shift frequency, are transmitted to the receiver circuit to set up in the resonant circuit included therein an alternating current of this frequency, which as described above is used to energize the signal translating device 42.

An alternative design of signal translating device is shown in Fig. 7. In this figure corresponds with that of the interrupter or commutator of the transmittingstation, this translating apparatus will be actuated to indicate signals. I In Fig. 8,. an arrangement including balanced electrondischarge devices is shown which may be substituted for the signal translator. or receiver circuit arrangement previously described, by connecting the points A and B of the input circuits of the devices73 and 74 with lettered cuits. i i

When no signals are being received, the potential across the plate circuits of the tubes 73 and 74 is sup ied by a common battery and hence e u" y currents will flow in these circuitsqwit out afiecting' the receiver 42. Incoming groups or trains of signal waves. of one signal frequency will cha'nge the potential applied to the control element of the device 73 and thereby cause variatioh in-the currentflowing in its plate circuit. Similarly, trains of waves of the other signal frequency will efi'e'cta change in the potential applied to the control element of the device 74 and consequently va "the current flowing in its plate circuit. lilhder the control of the transmitter interrupter, these current impulses will occur alternately in the t circuits oft'he devices 7 3 and 74 at the shift fre uency rate to which the circuit 75 associate therewith is tuned, and hence an alternating current of the shift frequency will. be setru in the circuit 75. This circuit is included in the input circuit of an amplifier 76, in the output circuit of which the receiving device 42 is included.

Receiver arrangements of the design shown in Figs. 7 and 8 may be substituted for that shown in Fig. 3, since they will only be energized when signal waves of predetermined frequencies recurring at the selected shift frequency are employed. 7

, From the preceding description it will be seen that the signal translating device can only be-actua ted when Signal waves of selected frequencies and alternating at a definite rate are incident upon the antenna. Oscillations set up in the antenna circuit at the receiving station by static disturbances will either balance one another or their rate of alternation will difler from theshift frequency, and, as a consequence, they will not the correspondingly poi-ntsin the receiving station cirit These coils are actuate the receiving device. Again, under any given operating conditions, interfering stations would have to employ not only the same wave frequencies to identify signal impulses, but these waves must also recur at the shift frequency rate.

The last mentioned type of interference, should it occurn may be readily eliminated by varying one of the signal frequencies employed or by varying the rate at which these frequencies are alternately transmitted. In the first case a corresponding adjustment will have to be made in the selective circuits at the receiver station, while in the latter, the tuning of the receiver control element will have to be adjusted tocorrespond with the new shift frequency used.

Furthermore, though the preferred shift frequency rate is herein stated to be within the range of audibility, it is not necessarily so limited, since, as is well known, waves alternating at an inaudible frequency may be used to control the supply of audible frequency current to the signal translating device at the receiving station.

lVhile certain specific details and elements have been described with the object of clearly and completely disclosing the principles of the invention, and its application to radio telegraphy has been disclosed, it Will be appreciated that the principles utilized are independent of the meansherein shown and described and therefore they may be applied to low frequency carrier or radio frequency systems. It is therefore to be understood that this invention-is not limited to the are rangement herein disclosed but only by the scope of the attached claims. l i

lVhat is claimed is:

1. A telegraph system comprising means for transmitting signal waves of different frequencies alternately recurring at a definite frequency, means at the receiving station for producing wave trains of different frequencies differing from the incoming waves, and means for producing from said wave trains an alternating current of said definite frequency.

2. A system in accordance with claim 1 comprising a sound producing indicator operated by said last mentioned current.

3. A telegraph system comprising means for transmitting signal waves of different frequencies alternately recurringat a definite frequency, means at the receiving station for producing wave trains of frequencies different from the incoming waves, and means controlled by the joint action of said Wave trains for producing an alternating current of said definite frequency.

4. In a signaling system employing a car rier wave modified by non-simultaneous wave trains recurring in regular sequence,

trains, comprising a carrier wave circuit, a low frequency circuit, sald carrier ClI'CUlt comprising means for detecting carrier waves received thereover to derive said alternately recurring wave trains, and means for producing in said low frequency circuit an alternating current of the same frequency as the rate of alternation of. said wave trains.

6. In a signaling system, means for transmitting a carrier wave, means for modulating said waves at a plurality of'frequencies in cyclic order ata definite period of cyclic recurrence, in combination with a receiver selectively responsive to the carrier frequency *and each of the plurality of he quencies, a low frequency circuit, and means for producing in said low frequency circuit an alternating current of the same frequency as the cyclic recurrence of said plurality of frequencies. i

7. A carrier telegraph system comprising means for transmitting a high frequency wave modulated by waves of different frequencies successively applied at a definite frequency, means for receiving said modulated wave and deriving therefrom said Waves of different frequencies, means for selecting said waves of different frequencies,

a low frequency circuit, and means, controlled by said waves of different frequencies, for producing in said low frequency circuit an alternating current of said definite frequency for controlling a an indicator.

8. A carrier telegraph system comprising meansforfltransmitting a high frequency wave modulated by waves of different frequencies applied alternately, means for receiving said modulated Wave, means for detecting and separating said waves of different frequencies, a 10W frequency circuit,

means for producing in said low frequency circuit a current of the same frequency as the rate of alternatlon of said waves of different frequencles, a sound producing indicator, and means for controlling said indi cator by the current in said low frequency circuit to produce a toneof corresponding frequency.

In witness whereof, I hereunto subscribe my name this 29th day of November A.D.,.

LEWIS M. CLEMENT. 

